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the 21 cm hydrogen line. Once the atoms enter the resonance cavity, they find other atoms radiating and they fall in step. They "start to talk to each other" and echo what they hear. This produces a highly coherent oscillation. This is the signal to which the crystal oscillator is phase-locked. All of that is packaged in cabinets with power supplies, temperature control, and magnetic shielding.
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The storage bulb is a quartz bulb about 20 cm tall which is coated inside with Teflon to control the recombination rate of atoms into molecules. The quartz bulb is located in a precisely machined pure copper cylinder which acts as a microwave resonant cavity for the 1.420 GHz frequency of
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Both the proton and electron of a hydrogen atom have spins. The atom has a higher energy if both are spinning in the same direction, and a lower energy if they spin in opposite directions. The amount of energy needed to reverse the spin of the electron is equivalent to a photon at the frequency of
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for the cavity. With advanced microwave cavities made out of silver-plated ceramic, the gain factor can be much higher, thereby requiring less hydrogen atom density. The active maser is more complex and more expensive but has better short-term and long-term frequency stabilities.
123:. Adsorption onto, chemical interaction with, and perturbation of atomic state by the bulb surface is much reduced. Consistent interactions with the bulb increase the quality of the oscillation. A durable PTFE and bulb coating technology allows for over 20-year lifetime.
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sublevels. To decrease the influence of changing external magnetic fields on the transition line frequency and be compliant to electromagnetic interferences, the cavity is surrounded by several nested layers of shields.
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frequency. The external frequency is tuned to produce a maximum output in the cavity. This allows the use of lower hydrogen atom density and lower cavity quality factor, which reduces the cost.
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resonance frequency of the atoms. A weak static magnetic field is applied parallel to the cavity axis by a solenoid to lift the
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In the active hydrogen maser, the cavity oscillates by itself. This requires a higher hydrogen atom density and a higher
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made from a precisely machined copper or silver-plated ceramic cylinder. This cavity is tuned to the
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then a magnetic state selector and into a storage bulb. The storage bulb is roughly
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Kleppner, D.; Goldenberg, H.M.; Ramsey, N.F. (1962). "The Atomic
Hydrogen Maser".
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Bauch, A. (2007). "Atomic frequency standards, properties and applications". In
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In the passive hydrogen maser, the cavity is fed from an external
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Hydrogen masers are very complex devices and sell for as much as
80:. There are two types to be distinguished: active and passive.
357:, "Active Hydrogen Maser Atomic Frequency Standard"
387:. Vol. Course CLXVI. SocietĂ Italiana di Fisica.
43:atom to serve as a precision frequency reference.
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182:A passive hydrogen maser used as a clock in
262:"MHM 2010 Active Hydrogen Maser Data Sheet"
39:that uses the intrinsic properties of the
83:In both types, a small storage bottle of
381:; Leschiutta, S.; Wallard, A.J. (eds.).
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384:Metrology and Fundamental Constants
233:"Time and Frequency from A to Z: H"
184:Galileo satellite navigation system
16:Device used as a frequency standard
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456:Hydrogen Maser Frequency Standard
213:Timeline of hydrogen technologies
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391:: IOS Press. pp. 303–308.
325:United States Naval Observatory
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126:The storage bulb is inside a
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23:Diagram of a hydrogen maser
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73:in the hydrogen spectrum.
198:A hydrogen maser used by
170:An exposed hydrogen maser
31:, also known as hydrogen
115:in diameter and made of
35:, is a specific type of
442:10.1103/PhysRev.126.603
321:"USNO, Hydrogen Masers"
119:internally coated with
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482:Electronics standards
472:Hydrogen technologies
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434:1962PhRv..126..603K
477:Laser applications
237:Physics Laboratory
85:molecular hydrogen
33:frequency standard
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398:978-1-58603-784-0
103:passes through a
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243:. Hydrogen Maser
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138:of the magnetic
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128:microwave cavity
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101:atomic hydrogen
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71:21 cm line
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156:1.420 GHz
148:quality factor
132:1.420 GHz
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29:hydrogen maser
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458:- Honeywell
269:Symmetricom
78:US$ 235,000
466:Categories
428:(2): 603.
412:2010-04-08
407:2007934139
355:US 5838206
335:31 January
306:2010-04-08
275:31 January
247:2010-04-06
219:References
136:degeneracy
113:10 cm
109:20 cm
105:collimator
389:Amsterdam
111:high and
207:See also
200:BeiDou-3
47:Overview
41:hydrogen
430:Bibcode
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271:. 2014
140:Zeeman
117:quartz
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265:(PDF)
54:1.420
37:maser
403:LCCN
393:ISBN
337:2016
277:2016
241:NIST
121:PTFE
438:doi
426:126
66:GHz
62:768
59:751
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